Sewage utilization instead of sewage treatment
Béla Tolnai
mechanical engineer
Key words: sewage utilization, sewage treatment, modelling of biological filtering
1
SEWAGE GENERATION AND COLLECTION
There are several definitions of the term sewage or, with other words, wastewater known.
Wikipedia provides the following definition1:
Wastewater is the end-product of industrial or communal water consumption;
essentially it is any kind of water that has been polluted to the effect of anthropogenic
impact or, respectively, its original quality has degraded.
This explanation considers pollution as a fact, although pollution of the entire amount of water
does not necessarily come forward.
We use water in the households in order to make our life easier and raise the quality of life
when flush off “contaminations” generated in the flat.
toilet
rainwater
kitchen
bathroom
laundry room
1-1. Generation of household sewage
Contamination is generated in different places in the household. Waste disposal from the toilet,
the laundry room, the bathroom and the kitchen is carried out uniformly by water. At the
moment of wastewater generation these waters are still separated. They will be mixed by being
discharged through a common sewerage. Water first of all has got a logistic role in this
discharging process: it carries off the generated contamination. During this process water - due
mainly to diluted matters - becomes used and polluted.
1
http://hu.wikipedia.org/wiki
1 / 12
The so called blackwater generated in the toilet is heavily charged. Charging is due to the high
organic matter content of faeces and urine. Blackwater has got a small proportion in sewage.
On the contrary, greywater generated in the bathroom, laundry room and kitchen is low charged
and its quantity is significant. Leaving the premises blackwater and greywater is mixed in the
sewerage and becomes household sewage.
100
80
60
40
20
0
Greywater
Urine
Faeces
Blackwater (urine + faeces) contains
99% of bacteria, 98% of nitrogen and 90% of phosphorus.
Source: Tolilettes Du Monde, 2009
Figure 1-2. Composition and quantity of communal wastewater
qu
Composition and quantity relations of Figure 1-2. are clear. They indicate the inexpedience of
mixing. Stormwater accumulating on the roof is basically not polluted, but - as it is shown in
Figure 1-1. - it will become that by mixing when discharged into the sewer.
On the way towards the sewage treatment plant industrial wastewater and stormwater from the
streets is added to the household sewage. The resulted mixture has been generated by us and
then at the sewage treatment plant we concentrate with all endeavours on how to separate the
components of the mixture from each other. For this reason one can hear more and more about
the separate collection of blackwater and greywater preventing them to mix.
At the time of wastewater generation the minimization of tap water use may be targeted, as
well. In this case the once already used and recycled greywater is used for flushing the toilet,
which recycling can be implemented in the household. As a consequence the amount of sewage
discharged from the household will be less, but it will be more charged as less water carries off
the same amount of contamination. Seemingly it is an effective solution subduing the use of tap
water. In the sewerage, however, transportation of suspended solid particles can be effective
only over a certain flow rate. At low flow rates sewerage sedimentation leads to block that may
cause the failure of wastewater disposal. While we need to work toward rational water use we
have to admit that a certain amount of water is needed in the sewerage.
Sewerage service consists of two parts: sewage disposal and sewage treatment. We are
talking of sewage disposal, while actually it is the discharging of waste generated in the
households and the industry by flushing it with water. In this process water has got only a
logistic role of transportation.
In the sewerage waters of different quality charged to a different extent are mixed. At the
sewage treatment plant in course of the treatment process we try to separate the components of
this mix. At this point the obligatory question to ask is the following: Why to mix it if we have
to struggle with separation later on?
Mixing could be prevented by the use of separate sewerages. This idea is not newfangled, but
the construction would have a large investment cost. In spite of this the demand for separate
collection comes to the view more and more.
2 / 12
It would be difficult to implement separate wastewater disposal or separate collection in a
densely populated urban environment, but it might be feasible in a village. Collection of
blackwater by vacuum trucks and composting it later on may be profitable. Disposal of
greywater could be feasible even in open ditches, but closed pipes are better to the purpose.
Sewage treatment at the end of the sewerage system will thus be significantly easier.
Hereinafter let’s put an emphasis on sewage utilization instead of sewage treatment. This
seemingly minor bias, however, leads to the substantive revaluation of a range of things.
2
REINTERPRETATION OF SEWAGE TREATMENT
2.1 Sewage utilization in the case of separate collection
Separated sewerage systems have not been developed in the cities because of their large
investment costs. Posterior construction of separated sewage collection does not seem to be
economical either because there are difficulties in the long distance transportation of blackwater
due to large viscosity. Therefore, the establishment of local, complex utilization equipments of
small unit performance will gain ground.
Greywater can be utilized in two ways: one is heat recovery, and the other is using it for
irrigation water after treatment along with the collected stormwater.
Blackwater contains hardly any water. First biogas is generated by sludge digestion then the
gas is combusted in a gas engine. The gas engine needs to be cooled, thus heat energy is
generated which can be used for heating. The gas engine powers a generator and the produced
current can be reused in the household. Digested sludge will finally be composted. The compost
is used as an organic manure.
Today the solution shown in Figure 2-1. still might seem utopistic [5]. However, this form of
construction designed for housing estates has one important message as per only hardly polluted
greywater needs to be treated in a traditional meaning.
Stormwater
Blackwater
treatment
Greywater
treatment
Sludge
digestion
Biogas
Gas engine
Vacuum pump
220 ~
Irrigation water
Generator
Heat
exchanger
Blackwater
Greywater
Clean water
Storage tank
Heat
Current
2-1. Local sewage utilization
Greywater treatment is, however, a much simpler task.
2.2 Sewage utilization in large wastewater treatment plant
Today it is a general fact that a mixture of communal and industrial wastewater enters the
wastewater treatment plant through the common sewerage. The amount of wastewater is
increased furthermore by added stormwater. There have been many sewage treatment
3 / 12
Ozone dosing
Presedimentators
Cascade
aeration
Grid
Used water
technologies developed. The most common technology is the so called activated sludge
technology.
However, the world talks more and more about sewage utilization instead of sewage treatment.
Sewage utilization is not only a fashionable term; it is worth to pay attention to it. The point is
that everything what is useful in the wastewater has to be extracted. Consequently, the
utilization of the entire amount of sludge separated by (pre)sedimentation should be targeted.
Opinion is divided on whether sludge utilization would be equal to biogas production. Biogas
is generated by sludge digestion. It is composed of mainly methane (approx. 60%) and carbon
dioxide (approx. 40%). The heating value of a gas with such a composition cannot be compared
to that of the natural gas. By the extraction of carbon dioxide and other pollutants - first of all
sulphur - the heating value can be improved and thus the possible ways of utilization extend.
However, the gas purification process is expensive. Therefore, combustion in gas engines of
poor efficiency takes place as a common alternative. Gas engine powers generator which in
turn produces current. A part of the generated heat is used for heating the digestion towers.
Surplus heat can be used for other purposes. Digested sludge is compostable or may be enriched
with lignite.
Figure 2-2. also depicts the case when there is no biogas generation, i.e. the entire amount of
raw sludge is composted or stabilized by lignite in course of the LIGNIMIX process [4].
Composting usually takes place off the sewage treatment plant due to its large space demand,
while there is enough room to mix sludge with lignite on site.
Either along with biogas production or without that, sludge utilization should anyway serve
agricultural purposes, as well. Arable lands badly need organic manure supply. The safety of
crop production for food, however, demands that treated sewage sludge applied in the fields
shall not contain detrimental substances. This is the reason why an environmentally conscious
use of the sewerage system has to be encouraged.
The principle of “polluter pays” is basically right, just the term of polluter has to be revaluated.
It is not a polluter who discharges waste of communal origin into the sewerage system, i.e. uses
his or her sanitary equipment as it is intended to.
Biological filters
(Pe ~10)
Griddust
The whule
amount of
sludge
Wastewater
Aeration
Rinsewater
reservoir
Gas engine
Sludge
thickener
M
G
Generator
Heat-exchanger
Lignimix
granules
Emulsion
Digested sludge
Cavitron
(Desintegration)
Biogas storage
Row sludge
Reciver
Rinsewater
pumpstation
Sludge digestion
towers
Lignit
powder
Cleaned water
Dehydrating &
desiccative
equipment
Dehydrated sludge
Dehydrating
machine
Watewater treatment plant
2-2. Sewage utilization in wastewater treatment plant
4 / 12
Composting
Treatment of the residual decanted wastewater remains a task. As it has earlier been noted, the
today commonest activated sludge technology does not come to mind, as following the
separation of the entire amount of sludge the biofilm carrier flocculate is no longer available
for us. We need then a process which does not require sludge to be present for the water
treatment and an adequate biofilm carrier surface needs to be ensured separately.
Effective treatment of used water can be implemented at low Péclet number. Bank filtration (Pe
= 5 - 15) is suitable even for the retention of medicine residues [2]. By using artificial biological
filtering of similar parameters unwanted molecules can be extracted from the decanted
wastewater, as well. The quality requirements of disposal into natural waters getting stricter
and stricter can thus be fulfilled.
3
MODE OF
TREATMENT
ACTION
OF
BIOLOGICAL
WASTEWATER
As sewage utilization gains ground the basic duty does not change; only it is not wastewater
but greywater or decanted wastewater that has to be treated, depending on the formerly shown
arrangements. The theory of biological filtering leads us to an answer to these tasks without
using sludge.
The modelling of bank filtering leads to a general structure [1] that can be considered as the
axiomatic foundation of the theory of biological filtering. We can state the following:
 A solid surface is needed for biofilm adhesion.
 The treatment process consists of three consecutive processes. Convective flow or
leakage conveys pollutant to the biofilm. Conductive flow or diffusion detaches
pollutant from the main flow and ingests it into the biofilm. Logistic stages based on the
principles of flow technology are preconditions to the processes taking place within the
biofilm.
 Nutrient decomposition takes place within the biofilm.
Convective material flow,
persolation
Conduktive material flow,
diffusion
Biochemical process,
Nutrient decomposition
Condition (driving force)
Maintened by
Pressure difference
Pumping, mixing
Concentration difference
Bacteria s work
Solid surface for biofilm adhesion,
Redox envinronment
Bacteria s instict
Feedback
Serial
process
Sub-process
3-1. Consecutive elements of biological filtering and feedback
Table 3-1. shows the momentum of each sub-processes as well as the way how to maintain
them. Leakage occurs in the deposit to the effect of pressure difference which is maintained by
pumping or mixing. Diffusion is driven by the concentration difference.
Nutrient decomposition is a biochemical action which converts the molecule entering the
biofilm thus “eliminating” its concentration within the biofilm. Concentration difference
outside of and within the biofilm is thus continuously reproduced.
Diffusive motion comes off uniformly in all directions of space such as it can be observed in
the case of Brownian motion. Ions move also according to the principle of diffusion. By the aid
of an electric field, however, the charged particles can be diverted into one direction. In order
to differentiate it from spontaneous diffusion this directed motion is called drift. In our case a
one-way diffusive motion from the water towards the biofilm can be observed. The momentum
is provided by a continuously reproduced concentration difference due to the bacteria’s
activity.
5 / 12
In Table 3-1. the life instinct of bacteria means the force that induces them to decompose
nutrients. In terms of systems engineering decomposition induces a feedback by the
reproduction of a concentration difference.
3.1 Logistic criteria of biological filtering
Efficiency of nutrient decomposition in logistic terms is also determined by the size of the
surface that can be colonized by bacteria. To decompose a large amount of nutrients a large
number of bacteria is needed which, in turn, are able to adhere only to a large surface. The
larger the surface size in a given volume is the smaller the size of the biofilm carrier particles
are.
The logistic criteria of biological filtering are characterized by the Péclet number as follows:
Pe =
w dm
DS .
where w [m/s]
dm [m]
is the filtering rate
is the standard particle diameter
(in the case of sand filter it is equal to the typical particle
diameter)
Ds [m2/s]
is the diffusion factor of substrate (the decomposable pollutant)
The Péclet number is a dimensionless number. It includes three different characteristics: the
most important parameter of operation, i.e. filtering rate (w), the quality of water to be treated
characterized by the diffusion factor of the pollutant (Ds), and the specific characteristic of the
filtering substrate or the biofilm carrier deposit, i.e. the particle diameter (dm), which refers to
the size of the carrier surface.
The Péclet number is originally interpreted as the ratio of convective and conductive currents.
The precondition of effective decomposition in this approach is that the nutrient that arrives to
the biofilm is able to penetrate into it, i.e. the desired value is Pe ~ 1.
There is another, more illustrative interpretation. After an algebraical conversion of the fraction
we get the following form:
The result is the ratio of the time needed to take the dm long diffusion way and the retention
time spent in front of the dm sized biofilm carrier particle.
The precondition of effective decomposition is when these two periods of time are nearly equal
to each other (Pe ~ 1). When Pe<1 then no sufficient amount of nutrient arrives to the biofilm,
while when Pe>>1 then the nutrient passes away quickly in front of the biofilm instead of
getting ingested.
The calculation of the Péclet number seems to be easy. However, in the case of different sewage
treatment processes there are significant difficulties in the interpretation and determination of
the given factors. Some geometric considerations may be necessary in order to determine the
equivalent de and the standard dm particle diameters [1].
Pe =
6 / 12
Grain of sand d m = de = 1,3 * 10-3
Danpak dm=de= 1,7 * 10-3
Ultra filter d m=de= 2,7 * 10-3
WasserCare d m = de= 7,7 * 10-4
Floc size (activated sludge) dm = de= 1 * 10-4
Hair h = 8 * 10-5
Arbitrary size limit dm := 5*b = 1,2 * 10-5
Size of microbes b = 2,5 * 10-6
7
Zeolite de= 5,9 * 10-7
Light microscope h=2*10-
Macromolecules d=(3-100)*10-9
Activated carbon de= 7,5 * 10-9
Molecules d=(4-60)*10-10
Size of atoms d=(1 - 5) * 10-10
lg d [m]
10-10
10-9
[Å]
[nm]
10-8
10-7
10-6
10-5
10-4
[μm]
10-3
10-2
10-1
1
[mm]
[cm]
[dm]
[m]
dm = 5*b
dm = de
3-2. Equal and standard particle diameters
Based on the equal and standard particle diameters the biofilm carrier substrates can be lined
up. The applied logarithmic scale indicates that there is a large distance between the sizes
representing some of the filtering substrates. It can be seen that the plastic biofilm carrier
products (WasserCare, Danpak) available in the market at the present still lag behind the
demands, and their specific surface is rather small. Bacteria are not able to fully colonize the
large specific surface of activated carbon and zeolite due to the bigger size of those.
3.2
Kinetics of biochemical processes
3.2.1 Metabolism of cells
Nutrient decomposition within the biofilm - if we only state that it has happened - seems to be
simple. If we have a closer look at it, we get a more diverse picture. It is worth to recall briefly
the activity mechanism that has already been justified by biologists for a long time in order to
better understand systems engineering relations.
The metabolism of cells can be described by the Michaelis-Menten enzyme kinetics (Table 33/A). As a solution of a differential equation system we get a relation referring to the reaction
rate - the rate of product generation - depending on the substrate content (Table 3-3/B). The
model is simple and provides a good phenomenological description of the phenomenon.
Parameters vmax and Km are easy to measure.
7 / 12
A
B
vmax
k1
k2
E + S 
ES 
 P+E
k1
E
S
ES
P
enzyme
substrate
complex
product
vmax / 2
0
C
Km
[S]
D
Substrate
The enzyme s shape changes
as soon astha substrate is
adsorbed
End-products
Without enzyme
Active centre
Energie
Eaktiválási
Substrate
With enzyme
Eaktiválási
ΔE
The substrate
enters the
enzyme s active
centre
Enzyme-substrate
complex
Enzyme and
end-product
complex
The end-products leave the
enzyme s active centre
(the enzyme recovers its
original shape)
Product
Reaction time
3-3. Enzyme kinetics
The theory elaborated at the beginning of the 19th century justified the role of enzymes in the
process illustrating the mechanism of molecule decomposition by geometric structures. A given
enzyme is able to decompose only a given type of substrate. This is indicated by the “key fitting
the lock” geometric forms in the figure. In order decomposition would be accomplished the
given enzyme has to be present in the space (Table 3-3/C).
Similarly to every living organism cells also need energy to sustain their vital processes. They
gain this energy from the decomposition of the substrate. Energy released in course of the
exothermic process ensures cell activity. Enzymes take part in this process as catalytic agent.
To their effect the activation energy needed for the decomposition will be significantly less
(Table 3-3/D).
From our biological studies we may know that decomposition takes place in more than one
step. This type of multistep process is the consecutive stages of nitrification and denitrification.
The product generated in the first reaction becomes a substrate in the next stage. Gradual
decomposition may have the risk of getting the process stucked somewhere, not being
completed and leaving behind undesired, maybe even toxic matters in the water.
In practice decomposition processes used to be described by stoichiometric equations. The endproduct is mostly water and carbon dioxide which may be apostrophized as that of an oxidative
burning process. Energy released in course of the reaction, however is not typically heat energy
as it is general at burnings with flame - but chemical energy from which the cell gains energy
needed for its activity and life subsistence. Gaining energy necessary for life subsistence may
be considered as life instinct.
Mechanical screening retains pollution while biological filtering “burns” it. Mechanical screens
needs to be regularly cleaned. On the contrary, biological filters are self cleaning.
3.2.2 Microbial reproduction
Bacteria are single-celled organisms. Their body builds up of protein, nucleic acid, lipids and
water. A significant part of the protein content is enzyme protein.
Bacteria, such as all other living organisms, have an important characteristic: namely that they
are able to reproduce. The most frequent form of reproduction is reproduction by fission. To
8 / 12
the analogue of the Michaelis-Menten enzyme kinetics, the kinetics of microbial reproduction
was developed by Monod some fifty years later in 1949.
A
B

900
n=0
x = x 0 2n
n=2
 x0ee
x=
700
600
dx
= μM x
dt
n =1
n: the number of generations
μ
tMt
800
x [-]
x
Microorganism
dividing by binary
fission
Fundamental
relationship of microreproduction
x
500
400
300
200
100
n=3
0
0
5
10
15
óra
t [h]
idő
n=4
Exponenciális
növekedés
X0=2
és μ=0,5
Exponential
growth
x0=2,
µM=0,5
C
D
dx
 x
= μM x  1 - 
dt
 K
x=
K
Mt
1 + x 0xe-μ=
K
1 + x 0e-μM t
μ M = μ M,max
The logistics function
S
KS + S
µM [1/h ]
x [-]
t [h]
S [g/L ]
K=800 x0=399, µM=0,5
3-4. Kinetics of microbial reproduction
Binary fission (Table 3-4/A) can be described by a differential equation, as well. The constant
μ
is a coefficient characteristic to a reproduction of relative growth M , which shows the increase
rate of subsequent generations. The solution of the differential equation results in an exponential
function. The function keeps to the infinite as time increases (Table 3-4/B). In the case of closed
systems a finite growth is realistic. The solution of the corrected - “slowed down” in growth differential equation will be the so called logistic function (Table 3-4/C).
μ
The M size of the exponent can be determined by measurement. Its value, depending on the
substrate content, shows saturation characteristic. Similarity can be detected then in the
development of the reaction rate of the Michaelis-Menten kinetics and the substrate dependence
of the Monod kinetics exponent. The upward rise of the curves can be characterized by the
provision of semisaturation constants (Km, Ks).
μ
The growth rate of microbes is of the order of an hour. Although the saturation value M ,max
becomes larger along with the increase of dissolved oxygen content in the water the growth rate
depending on the substrate content - the rise of the saturation curve - does not substantially
change. (Table 3-4/D). The rise of the saturation curve is determined by the type of the substrate
and the reproducing bacteria species, respectively.
Biofilm is not a timely static formation; it has dynamics.
9 / 12
Destruction phase
Accelerating growth stage
Dispersion
LAG stage
Growth
Stationary phase
x
Adhesion
Decclining phase
B
Exponential phase
A
x0
Time
3-5. Reproduction and mortality
Growth stages are distinguished. Accelerating growth stage, then declining and stationary
phases are followed by the death phase. Death can be related with dispersion (see Table 3-5/A
and B).
The reproduction or growth stage can also be described with the help of the logistic function
(Table 3-4/C). For this x0, K and μM parameters have to be selected and marked off.
3.3 Theory of biological filtering
Biological filtering is a complicated biochemical process where nutrient decomposition
depends on several variables. The function relation between variables was defined by using
dimension analysis [1]. The mathematics- and physics-based process starts with listing the
substantive variables. In the first step we reduce the number of variables by generating
dimensionless figures. In the case of the model is derived for bank filtration we get six
dimensionless figures, from among which Péclet number and L/d geometric ratio have a
substantial role (Table 3-6/A). These can be changed substantially by the operator.
A
B
ΔS = μ(Pe) CO2
1
L
Sc rH
Pe
d
Nutrient decomposition
Range of bankfiltration
Filtering factor
3-6. The relations of nutrient decomposition
The methodology of dimension analysis makes it possible to interpret the function relation
describing the phenomena, as well. According to the formula that can be described by heuristic
means (Table 3-6/B) nutrient decomposition is inversely proportional with the Péclet number
and is directly proportional with the L/dm ratio.
Illustrating the resulted formula as a function of the Péclet number - depending on the size of
the other factors - we get a host of hyperbola. In the range of very low Péclet number the grade
of nutrient decomposition with a constant filtering factor would be infinite, which is impossible.
Assuming the existence of μ = μ(Pe) function relation the unbounded growth of hyperbolas is
10 / 12
reversible. Starting off from the two-grade materialization of biofilm nutrient supply - nutrient
transport to the biofilm then its ingestion into the biofilm - let us identify formally the filtering
factor with the logistic function of microbial reproduction (table 3-4/C), namely let it be
β
μ := μ(Pe) :=
1 + a e- b Pe .
where
β is the proportional part of the filtering factor, the size of which can be determined by
measurement, and where
by the correct selection of a and b parameters near the value of Pe = 1 the maximum
value of the function, while at Pe = 0 the nearly 0 function value can be reached. (By
selecting the values of a=100 000 and b=12 - according to our expectations - the infinite
characteristic of hyperbolas will disappear, the maximum value of the function will be
near 1 and the nutrient decomposition curve will intersect the y-axis near the pole (Table
3-6/B).
Having provided the filtering factor the theory of biological filtering has been completed.
Summarizing our foregoing results we can state that theories build on each other. Figure 3-7
summarizes this.
A
B
Michaelis-Menten
kinetics
Monod kinetics
Theory of
biologocal filtration
Theory
What is it
about?
The place
of
occurrence
Key
parameter
MichaelisMenten
kinetics
Metabolism
of cells
Cell
Reaction
rate
Microbial
reproduction
Biofilm
Relative
growth factor
Biological
filtering
Biological
reactor
Monod
kinetics
Enzyme
Bakteria
Semi-saturationfactor
Logistical function
Theory of
biological
filtering
Filtering
factor
3-7. Interconnecting processes
The result of the Michaelis-Menten kinetics has inspired Monod when he was interpreting the
relations of microbial reproduction. For the description of reaction rate on the one hand, and
that of the relative growth rate on the other hand, functions of the same shape are used. At both
kinetics it is the enzyme that embodies the conceptual similarity.
The microbial reproduction equation of the Monod kinetics carried out in a closed space, the so
called logistic function has lent its shape to the filtering factor of the nutrient decomposition
model. Setting a colony of bacteria reproducing according to the principles of Monod kinetics
and supplying them with nutrients is the task of the process based on the theory of biological
filtering.
Through these steps can we get from the cells through the microbes to the events ruled by the
theory of biological filtering and finally to the clearing of water.
4
SUMMARY
Sewage utilization can be maximized if the total amount of sludge is disposed, as it is
recommended by the CARISMO process, as well [3]. This may be feasible, however, only if
the decanted wastewater can be treated without the involvement of sludge flocs. It is also
required that medicine residues shall be filtered already in the sewage treatment plant. By a
11 / 12
more effective treatment of decanted wastewater environmental aspects may better prevail.
Jekel-experiments [2] and the theory of biological filtering drafted here lay the foundation of
all this and make this possible.
Capacities will be fully exploited when the digested sludge is applied to arable land as it is
shown in Figure 2-2. in alternative forms.
This integrated approach, in addition to minimizing environmental pollution, can also provide
us with a source of energy. Sewage sludge utilized in arable land is not only manure for plants
but by improving the water retention ability of the soil it also helps to diminish the extreme
manifestations of climate change.
5
REFERENCES
[1] Tolnai, B.:
Chapters from the topic of biological filtration and application
4th International Symposium Re-Water Braunschweig, 06-07.11.2013.
[2] Jekel, I. – Grünheid,S.:
Ist die Uferfiltration eine effektíve Barriere gegen organische Substanzen und
Arzneimittelrückstände
GWF Wasser-Abwasser 148 (3007) Nr. 10.
[3] Weigert, B.:
Vom Klärwerk zum Kraftwerk
GWF Wasser-Abwasser November, 2014.
[4] Stadler, J.:
The LIGNIMIX technology for stabilization of municipal sewage sludge and liquid
manure
4th International Symposium Re-Water Braunschweig, 06-07.11.2013.
[5] Londong, J. et al:
Greywater (re)use options in a German urban context – necessities, challenges,
barriers
4th International Symposium Re-Water Braunschweig, 06-07.11.2013.
12 / 12